"""
Originally Written by Simon Josefsson <simon@josefsson.org>.
Copyright (c) 2006, 2007, 2008 Yubico AB

Python port of AES by Mads Kiilerich <mk@giritech.com> is Copyright (c) 2008 Giritech A/S

See the COPYING file for license.
"""

NUMBER_OF_ROUNDS = 10

RC = [0x1, 0x2, 0x4, 0x8, 0x10, 0x20, 0x40, 0x80, 0x1B, 0x36]

rijndael_sbox = [ 0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B,
        0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76, 0xCA, 0x82,
        0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4,
        0x72, 0xC0, 0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5,
        0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15, 0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96,
        0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75, 0x09, 0x83,
        0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3,
        0x2F, 0x84, 0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB,
        0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF, 0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D,
        0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8, 0x51, 0xA3,
        0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF,
        0xF3, 0xD2, 0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7,
        0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73, 0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A,
        0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB, 0xE0, 0x32,
        0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95,
        0xE4, 0x79, 0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56,
        0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08, 0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6,
        0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A, 0x70, 0x3E,
        0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1,
        0x1D, 0x9E, 0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E,
        0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF, 0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6,
        0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16 ]

rijndael_inv_sbox = [ 0x52, 0x09, 0x6A, 0xD5, 0x30,
        0x36, 0xA5, 0x38, 0xBF, 0x40, 0xA3, 0x9E, 0x81, 0xF3, 0xD7, 0xFB, 0x7C,
        0xE3, 0x39, 0x82, 0x9B, 0x2F, 0xFF, 0x87, 0x34, 0x8E, 0x43,
        0x44, 0xC4, 0xDE, 0xE9, 0xCB, 0x54, 0x7B, 0x94, 0x32, 0xA6,
        0xC2, 0x23, 0x3D, 0xEE, 0x4C, 0x95, 0x0B, 0x42, 0xFA, 0xC3,
        0x4E, 0x08, 0x2E, 0xA1, 0x66, 0x28, 0xD9, 0x24, 0xB2, 0x76,
        0x5B, 0xA2, 0x49, 0x6D, 0x8B, 0xD1, 0x25, 0x72, 0xF8, 0xF6,
        0x64, 0x86, 0x68, 0x98, 0x16, 0xD4, 0xA4, 0x5C, 0xCC, 0x5D,
        0x65, 0xB6, 0x92, 0x6C, 0x70, 0x48, 0x50, 0xFD, 0xED, 0xB9,
        0xDA, 0x5E, 0x15, 0x46, 0x57, 0xA7, 0x8D, 0x9D, 0x84, 0x90,
        0xD8, 0xAB, 0x00, 0x8C, 0xBC, 0xD3, 0x0A, 0xF7, 0xE4, 0x58,
        0x05, 0xB8, 0xB3, 0x45, 0x06, 0xD0, 0x2C, 0x1E, 0x8F, 0xCA,
        0x3F, 0x0F, 0x02, 0xC1, 0xAF, 0xBD, 0x03, 0x01, 0x13, 0x8A,
        0x6B, 0x3A, 0x91, 0x11, 0x41, 0x4F, 0x67, 0xDC, 0xEA, 0x97,
        0xF2, 0xCF, 0xCE, 0xF0, 0xB4, 0xE6, 0x73, 0x96, 0xAC, 0x74,
        0x22, 0xE7, 0xAD, 0x35, 0x85, 0xE2, 0xF9, 0x37, 0xE8, 0x1C,
        0x75, 0xDF, 0x6E, 0x47, 0xF1, 0x1A, 0x71, 0x1D, 0x29, 0xC5,
        0x89, 0x6F, 0xB7, 0x62, 0x0E, 0xAA, 0x18, 0xBE, 0x1B, 0xFC,
        0x56, 0x3E, 0x4B, 0xC6, 0xD2, 0x79, 0x20, 0x9A, 0xDB, 0xC0,
        0xFE, 0x78, 0xCD, 0x5A, 0xF4, 0x1F, 0xDD, 0xA8, 0x33, 0x88,
        0x07, 0xC7, 0x31, 0xB1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xEC,
        0x5F, 0x60, 0x51, 0x7F, 0xA9, 0x19, 0xB5, 0x4A, 0x0D, 0x2D,
        0xE5, 0x7A, 0x9F, 0x93, 0xC9, 0x9C, 0xEF, 0xA0, 0xE0, 0x3B,
        0x4D, 0xAE, 0x2A, 0xF5, 0xB0, 0xC8, 0xEB, 0xBB, 0x3C, 0x83,
        0x53, 0x99, 0x61, 0x17, 0x2B, 0x04, 0x7E, 0xBA, 0x77, 0xD6,
        0x26, 0xE1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0C, 0x7D ]

def xtime(b):
    return ((b << 1) ^ 0x11b) if (b & 0x80) else (b << 1)

def aes_decrypt_python(state, key):
    """
    AES-decrypt one 16-byte block STATE using the 128-bit KEY, returning
    the decrypted output.
    """
    assert len(state) == 16
    assert len(key) == 16

    # convert from string to arrays
    state = [ord(c) for c in state]
    key = [ord(c) for c in key]

    round_key = list(key) # copy
    for i in range(NUMBER_OF_ROUNDS):
        round_key[0] ^= RC[i]

        round_key[0] ^= rijndael_sbox[round_key[13]]
        round_key[1] ^= rijndael_sbox[round_key[14]]
        round_key[2] ^= rijndael_sbox[round_key[15]]
        round_key[3] ^= rijndael_sbox[round_key[12]]

        for j in range(4, 16):
            round_key[j] ^= round_key[j - 4]

    for i in range(0x10):
        state[i] ^= round_key[i]

    for i in range(NUMBER_OF_ROUNDS):

        # First row: 0 shift, 0 4 8 12
        state[0] = rijndael_inv_sbox[state[0]]
        state[4] = rijndael_inv_sbox[state[4]]
        state[8] = rijndael_inv_sbox[state[8]]
        state[12] = rijndael_inv_sbox[state[12]]

        # Second row: -1 shift, 1 5 9 13
        j = state[13]
        state[13] = rijndael_inv_sbox[state[9]]
        state[9] = rijndael_inv_sbox[state[5]]
        state[5] = rijndael_inv_sbox[state[1]]
        state[1] = rijndael_inv_sbox[j]

        # Third row: -2 shift, 2 6 10 14
        j = state[2]
        state[2] = rijndael_inv_sbox[state[10]]
        state[10] = rijndael_inv_sbox[j]
        j = state[6]
        state[6] = rijndael_inv_sbox[state[14]]
        state[14] = rijndael_inv_sbox[j]

        # Fourth row: -3 shift, 3 7 11 15
        j = state[3]
        state[3] = rijndael_inv_sbox[state[7]]
        state[7] = rijndael_inv_sbox[state[11]]
        state[11] = rijndael_inv_sbox[state[15]]
        state[15] = rijndael_inv_sbox[j]

        for j in range(15, 3, -1):
            round_key[j] ^= round_key[j - 4]

        round_key[0] ^= RC[NUMBER_OF_ROUNDS - i - 1] ^ rijndael_sbox[round_key[13]]
        round_key[1] ^= rijndael_sbox[round_key[14]]
        round_key[2] ^= rijndael_sbox[round_key[15]]
        round_key[3] ^= rijndael_sbox[round_key[12]]

        for j in range(16):
            state[j] ^= round_key[j]

        if i != NUMBER_OF_ROUNDS - 1:
            for j in range(0, 16, 4):
                k1 = state[j] ^ state[j + 2]
                a02x = xtime(k1)
                k2 = state[j + 1] ^ state[j + 3]
                a13x = xtime(k2)

                k1 ^= k2 ^ xtime(state[j + 1] ^ state[j + 2])
                k2 = k1

                a02xx = xtime(a02x)
                a13xx = xtime(a13x)

                k1 ^= xtime(a02xx ^ a13xx) ^ a02xx
                k2 ^= xtime(a02xx ^ a13xx) ^ a13xx

                state[j] ^= k1 ^ a02x
                state[j + 1] ^= k2
                state[j + 2] ^= k1 ^ a13x
                state[j + 3] ^= k2 ^ a02x ^ a13x

    return ''.join(chr(x) for x in state)


# When PyCrypto library is available use that because it's faster

try:
    import Crypto.Cipher.AES
except ImportError:
    aes_decrypt = aes_decrypt_python
else:
    def aes_decrypt_pycrypto(state, key):
        """
        Decrypt with PyCrypto - The Python Cryptography Toolkit from http://pycrypto.org/
        """
        return Crypto.Cipher.AES.new(key, Crypto.Cipher.AES.MODE_ECB).decrypt(state)

    aes_decrypt = aes_decrypt_pycrypto
